This invention relates generally to the field of chemical vapor deposition. In particular, this invention relates to the use of certain aluminum compounds for use in the chemical vapor deposition of aluminum films.
In the semiconductor industry, technological and material development have resulted in the miniaturization, high reliability, high speed, high functionality, and high degree of integration of devices, such as semiconductor integrated circuits. With the development of the manufacturing process of semiconductor devices, the development of improved memory devices, such as dynamic random access memory ("DRAM"), has been rapid. Currently, 64 mega DRAM is under mass production and, in the year 2,000, it is anticipated that with the new manufacturing methods of the next generation semiconductor devices, as well as with their mass production capabilities, 256 mega class memory devices may be available, as well as 1 giga ("G") and 4 G class high memory devices.
The next generation memory devices, those having high memory capacity, are the result of miniaturization of the memory device circuits; specifically, narrowing the line widths to 0.25, 0.18, and 0.15 microns (".mu.m").
The current wiring method in the semiconductor memory devices using aluminum as the wiring material is by vapor deposition, i.e., the sputtering method in which a metal, i.e. aluminum, itself is used for deposition to attain a desired thin film. This method limits the manufacturing process technology in achieving the narrowing of the line width described above.
In the manufacturing of 64 mega DRAM using aluminum (Al) metal wiring, the sputtering method has been the sole method used in the deposition of aluminum from an aluminum target. In the next generation memory devices described above, the circuit line width would be less than 0.25 .mu.m and the aspect ratio (depth/diameter) of contact and via hole is large in the vapor deposited metal, thus, the use of sputtering in the vapor deposition process would be unsuitable.
To alleviate such a problem, an aluminum wiring process using chemical vapor deposition ("CVD") method has been studied for a long time. This method has a high step coverage and has an improved burying process of contact/via hole, which is an advantage of the method. Thus, aluminum wiring from vapor deposition of aluminum ("Al-CVD" or aluminum chemical vapor deposition) will be the foundation of the technology for the production of the next generation class memory devices and the CVD method is considered to be the imperative method.
In aluminum film deposition using the chemical vapor deposition method, an aluminum compound, known as the precursor, was used as the source material. The chemical properties and the selection of the compound greatly affect the CVD process and they are the most important elements in the process. Therefore, prior to the selection of the deposition method, it is imperative that the selection and development of the precursor are the first factors to be considered.
In spite of the importance of the role of a precursor, the metal film deposition process using CVD method has developed concurrently with the use of the process in the manufacture of the next generation semiconductor devices. For this reason the development of the precursors for Al-CVD has been delayed.
In the early stage of Al-CVD method development, alkyl aluminum compounds were widely used in the industry. The typical alkyl aluminum compounds commonly used were trimethylaluminum, as represented by the chemical formula of Al(CH.sub.3).sub.3, and triisobutylaluminum, as represented by the chemical. formula of [(CH.sub.3).sub.2 CHCH.sub.3 ]Al.
In the nineteen-nineties, the development of precursors for aluminum film deposition using the chemical vapor deposition process was very active in Japan resulting in the development of dimethylaluminum hydride, represented by the chemical formula of [(CH.sub.3).sub.2 AlH].sub.2, and in the USA resulting in the development of dimethylethylaminealane, represented by the chemical formula of H.sub.3 AlN(CH.sub.3).sub.2 C.sub.2 H.sub.5. These compounds were leading precursors in the Al-CVD process.
Among the chemical compounds examined, dimethylethylaminealane was synthesized by Wayne Gladfelter of the University of Minnesota, in 1989, after the report of J. K. Ruff et al. in the Journal of the American Chemical Society, 1960. The synthesis of dimethylethylamine, (N(CH.sub.3).sub.2 C.sub.2 H.sub.5) has not been reported in the complex compound developed from aluminum hydride (AlH.sub.3) and an alkyl amine in the report. U.S. Pat. No. 5,191,099 (Gladfelter et al.) discloses dimethylethylaminealane as a precursor in Al-CVD process.
Other chemicals, such as dimethylaluminum hydride, trimethylaluminum, and triisobutylaluminum, have been developed and have been used widely in various applications since the nineteen-fifties. Specifically, dimethylaluminum hydride was reported by T. Wartik et al., Journal of American Chemical Society, 1953, 75, 835, and trimethylaluminum and triisobutylaluminum have been reported quite a bit earlier than the above.
These compounds have been fully commercialized and used in many industrial areas prior to the nineteen-nineties. They can be obtained economically, and they are liquid at room temperature, which are their advantages. However, the above-mentioned compounds have some problems when used as the precursors in the Al-CVD process. The film deposition temperature is above 300.degree. C. and near 400.degree. C. Due to this high deposition temperature, the vapor deposition process becomes very difficult and the high temperature deposition results in the inclusion of carbon impurities which increase the electric resistance of the deposited film, which are the detrimental flaws.
To alleviate such problems in the Al-CVD process, a dimethylaluminum hydride precursor and related technologies were developed in the early part of the nineteen-eighties. Dimethylaluminum hydride has a high vapor pressure (2 torr at 25.degree. C.) and its vapor deposition rate is high and it is a colorless liquid compound at room temperature. Also, advantageously, it provides very pure aluminum film deposition. However, dimethylaluminum hydride is an alkylaluminum compound that explodes when it comes into contact with air. Therefore, it is very difficult to handle and has high degree of difficulty in the manufacturing process which results in a low yield and high cost. Moreover, the vapor deposition temperature is 260-300.degree. C., which is a comparatively high temperature, and results in the high possibility of the inclusion of impurities in the thin film, which is also a disadvantage.
As alternative precursors in the Al-CVD process, the alane (AlH.sub.3) derivatives were used besides dimethylaluminum hydride. One of the alane derivatives, dimethylethylaminealane, forms a vapor deposition film of high purity at low temperature, 100-200.degree. C., according to the reaction described in Equation 1. Dimethylethylaminealane is a colorless chemical compound at room temperature and has a relatively high vapor pressure (1.5 torr at 25.degree. C.). In comparison with dimethylaluminum hydride, the flammability is somewhat less and it can be manufactured by a comparatively simple process at a low cost, which is advantageous. EQU H.sub.3 Al:N(CH.sub.3).sub.2 C.sub.2 H.sub.5 .fwdarw.H.sub.3 Al+N(CH.sub.3).sub.2 C.sub.2 H.sub.5 .Arrow-up bold.Al+3/2 H.sub.2 .Arrow-up bold. Equation 1
However, dimethylethylaminealane is thermally unstable at room temperature as well as during the vapor deposition process, which is carried out at 30.degree. C. Hence, during the storage the precursor gradually decomposes in the container. This difficulty in room temperature storage is a disadvantage. For this reason, development and reproducibility of the vapor chemical deposition process has been difficult in semiconductor device manufacturing processes.